In message  Chip Montrose writes:
>         Using the 543nm line of our Green HeNe laser, we have seen that our
 
> (1) The obvious question: what endogenous compounds are responsible for
> the red fluorescence.
 
In fixed tissue, lipofuscin fluoresces red under green excitation.  However, it
also fluoresces green under blue excitation (and far-red under red
excitation....)  Thus if what you're seeing is lipofuscin, it should be visible
using your fluorescein filters as well.
 
Lipofuscin accumulates with age--older animals are more likely to have problems
than younger animals.  Also, some tissues have more of it than others.  In
neurons, it has a granular appearance reflecting its presence in lysosomes.
 
Martin Wessendorf PhD, Asst Professor                [log in to unmask]
Confocal Microscopy Facility                            (612) 624 2991 (voice)
Dept Cell Biology and Neuroanatomy                        (612) 624 8118 (FAX)
University of Minnesota